RE: Move table online and update the indexes at the same time.
- From: "Mark W. Farnham" <mwf@xxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 27 Jul 2004 08:07:41 -0400
Please explain what you believe happens when you change the freelists for an
existing table.
I do not believe information regarding freelists is stored in individual
blocks, but rather freelists are lists of blocks queued up for new inserts.
Are you thinking of initial transactions and maximum transactions?
Further, I'm a bit confused that you're having freelist troubles due to
heavy update (unless you include insert in the generic "update" as opposed
to making a distinction between insert, update, and delete.) I suppose that
if the updates are something like a huge expansion of a row by putting a
giant lob into a column, then freelists might be called for in updates by
row migration and/or row chaining. If you routinely expand rows greatly, you
like have a different design consideration to consider re-tooling before you
spend a lot of time reorganizing.
good luck!
mwf
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Alexandre Gorbatchev
Sent: Tuesday, July 27, 2004 6:09 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: Move table online and update the indexes at the same time.
Tanel,
Yes, PCTUSED and PCTFREE needs to be corrected as well.
Yes, sure, we do have RAC. But even without RAC we experienced some
problems with low FREELISTS on heavily updated tables/indexes. Changing it
without reorg. would affect only new blocks. We need to change FREELIST
GROUPS and I was planning to set it higher than number of nodes we have
now in anticipation of additional nodes. Thanks for warning of the "side
effect" for setting several freelist groups - we have to research on it.
We can't easily partition some of the tables. I wonder what other options
are besides ASSM.
You've correctly pointed out the problem with IO distribution. That's
another reason for reorganization.
Thanks for your points,
Alex
From: Tanel Põder <tanel.poder.003@xxxxxxx>@freelists.org on 27-07-2004
12:44 ZE3
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Subject:
Re: Move table online and update the indexes at the same time.
> By the way, when is the lock required - in the beginning or in the end?
I've not tested it, but probably in the end, when you switch your newly
created table instead of the old one.
> I move the table for several reasons:
> 1.) CREATE TABLE ... AS SELECT produces the table which is much smaller
> (sometimes 2-3 times). We are trying to reduce the space usage with it.
So
> it seems the tables are space.
This seems to be an issue of incorrectly configured PCTFREE and PCTUSED.
If
you analyzed the table over time and checked the average free space in
blocks (and rowcounts+rowlens) you might get closer whats the real issue
here. In default configuration the tables PCTUSED is 40 for example,
meaning
that up to 60% of the block contents may remain empty and completely
unused
if the space usage doesn't fall below PCTUSED...
> 2.) Change storage clause - FREELIST, FREELIST GROUP or move to ASSM
(not
> sure, because it seems there are several bugs that we might hit in our
> environment)
You can change FREELISTS online without reorg. You shouldn't normally use
FREELIST GROUPS if you're not in OPS or RAC evnironment. Freelist groups
have the problem, that the processes which PID's map to another freelist
group, don't see free blocks in other freelist groups, thus potentially
wasting space in DML intensive environment. So if you're not seeing heavy
segment header block contention due freelist updates in your database, you
shouldn't consider freelist groups (and even if you see, then there are
other alternatives to consider, like partitioning, etc.)
ASSM - again don't move to it if you don't have a RAC environment (with
continuously changing number of nodes) or you don't have special
conditions
like having rows with extremely varying sizes inserted to your table etc..
> 3.) Physical layout reorganization. Some tables are in wrong
tablespaces.
This doesn't seem like a serious problem, given that your databases
availability is more important (unless you don't have serious bottlenecks
due improperly balanced IO)
Tanel.
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